The present invention relates to the conversion into useful products of heretofore considered useless waste and scrap rubber articles, particularly worn-out tires.
The long established prior-art practices for disposal of waste rubber have resulted in substantial pollution and degradation of the environment. Presently, there are in excess of 200 million used automobile tires discarded each year in this country. Even though some efforts have been made to reclaim and recycle small portions of this waste vulcanized rubber material through various methods and means, it is fair to state that currently no real productive uses exist for these discarded tires. Consequently, they are usually simply incinerated or placed in so-called sanitary landfills and even dumped into the oceans allegedly for the purpose of forming artificial barriers and reefs for the purpose of attracting fish. Obviously, these and other prior-art methods of disposal are at best stop-gap measures and cannot be allowed to continue indefinitely. In addition, such practices are indeed wasteful in that they do not go to the heart of the problem of recycling the valuable hydrocarbon values therein either as useful fuel or feedstocks to the petro-chemical industry and at the present time and in the foreseeable future such continuing wasteful practices indeed seem less than desirable, particularly in view of the demand for the likes of oil and natural gas. Accordingly, the potentially valuable hydrocarbon values in such discarded rubber articles would be better utilized if an economically attractive method for transforming them into useful liquid, solid, and/or gaseous hydrocarbon products having utility as fuel and/or as petro-chemical raw materials could be devised.
At the present time, there appear to be three general methods of approaching this desired objective to produce liquid or other fuels from discarded rubber articles such as worn-out automobile tires. One approach to the problem, to wit, the destructive distillation of scrap tires, was studied by the Bureau of Mines in cooperation with a segment of private industries and is reported in Bureau of Mines report No. 7302. In this approach, rubber was heated to temperatures between about 500.degree. and 900.degree. C and the volatile liquids and gases generated were collected. The chief disadvantage of this approach appears to be the amount of time required for the process to generate useful products in that heating times in excess of three hours were required. A second disadvantage to this approach was that the feed to the process was ground-up rubber rather than intact tire carcasses or relatively large "diced" pieces thereof. In another approach to the problem, researchers have attempted to apply oil shale retorting technology to the problem at hand by introducing into retort vessels shredded rubber. They estimate the cost of preparing the shredded rubber at $10.00 per ton. Aside from other disadvantages of this approach, a recent Rubber Manufacturers Association study indicates that the cost of preparing 16-mesh granulated rubber is about $43.00 a ton.
In still another approach to the problem, there is taught in U.S. Pat. No. 3,704,108 (Alpert) the catalytic hydrogenation of scrap tires wherein they are stirred in an autoclave reactor under hydrogen pressure ranging between about 500 to 2000 psig and temperatures ranging between about 660.degree. and 850.degree. F. The principal objective of this approach is to recover carbon black from the tires which is intended to be the principal product for sale. However, as it turns out, the resulting carbon black apparently contains sufficient ash that there appears to be no ready market for the principal product of this process. Aside from the relatively high pressures which necessitate an autoclave-type device, the cost of operating the process is also increased by the necessity of hydrogen as feedstock and the fact that expensive shredded rubber must be used.